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| Home > Publications database > Diffuse Neutronenstreuung an Verzerrungsfeldern von substitutionell und interstitiell gelösten Fremdatomen in Metallen |
| Book/Report | FZJ-2018-00366 |
1975
Kernforschungsanlage Jülich, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/16515
Report No.: Juel-1158
Abstract: The measurement of the elastic and quasielastic diffuse scattering of neutrons has been used to investigate the atomic configuration in the immediate neighbourhood of substitutionally and interstitially soluted defect atoms in metals. A spectrometer is being described which, by matching the resolution and by applying a time-of-flight analysis to the scattered neutrons has been designed to enable such investigations also in cases of small concentrations of weakly distorting defects and athigh sample temperatures. To describe the lattice distortions theoretically and to calculate the scattering cross section resulting from the displacement of the host atoms, the method of virtual forces is used, where the influence of the defect is described by a short ranged force-field. To compute the Fourier transform of the displacement field, which enters the expression for the scattering cross section, the coupling constants of the pure host material are used. A comparison of experimental data for the system $\underline{Al}$Cu to the results of model calculations showed that the assumption of forces of equal maqnitude on the 12 nearest neighbours alone is sufficient to describe the $\kappa$-dependence of the scattering cross section satisfactorily. A more complicated case is encountered in the system $\underline{Al}$Mn. Here the best description of the measured data could be achieved by a model with extremely anisotropic forces, in which the whole ofthe lattice contraction is practically due to the tight binding of two adjacent Al-atoms to the Mn-atom (off-center model). lt should be emphazised, however, that such a model would need additional experimental support. To investigate the distortion scattering in the Nb-H-system, deuterium has to be used as defect. Due to the fact that, because of the high mobility of the defects in this system, the scattering is quasielastic, the intensity scattered by D in Nb was compared to that obtained from H in Nb in order to avoid difficulties arising from the integration range as well as from geometry effects. At the same time this procedure has the advantage of lowering the influence of the abnormal Debye-Waller-factor, which, in turn, was measured at several temperatures.
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